Misoperation Scenarios and Preventive Measures for Extruder Screws (Including Emergency Handling for Sudden Power Outages)

The extruder screw is a core component. Misoperations can cause screw wear, deformation, fracture, and even lead to equipment downtime and safety accidents. Combined with the PVC/TPU pipe extrusion production scenarios, emergency procedures for unstable customer power supply and sudden power outages are added, and common misoperations and corresponding preventive solutions are improved as follows:

I. Misoperation Scenarios and Preventive Measures Before Startup

1. Starting up directly with new materials without cleaning residual materials in the barrel/screw

• Misoperation Manifestation: Without cleaning the high-temperature degraded materials and foreign objects (such as metal shavings, agglomerated materials) left from the previous batch production, new materials (e.g., PVC pellets) are directly added for startup, resulting in jamming and wear during screw rotation.

• Hazards: Dry friction occurs between the screw and the inner wall of the barrel, which will light damage the screw coating, or severely cause screw bending and barrel scratching.

• Preventive Measures

1. After each material change/shutdown, the barrel cleaning procedure must be implemented: First, rinse the barrel and screw with transition materials (such as HDPE) to discharge residual materials; if the residual materials have carbonized, the screw must be disassembled for manual cleaning (use copper brushes and scrapers, and avoid using steel wire brushes to scratch the screw surface).

2. Check the hopper to ensure no foreign objects before startup, and install magnetic frames and screens to filter metal impurities and agglomerated materials.

2. Starting up blindly without checking the clearance between the screw and the barrel

• Misoperation Manifestation: The coaxiality is not tested after screw installation, or the clearance becomes too large/too small due to screw wear after long-term use, but the startup is carried out without adjustment.

• Hazards: Excessively small clearance will cause friction between the screw and the barrel; excessively large clearance will lead to uneven plasticization of materials and easy vibration deformation of the screw.

• Preventive Measures

1. After new machine installation or screw disassembly, use a feeler gauge to detect the radial clearance between the screw and the barrel to ensure it meets the requirements specified in the equipment manual (usually the clearance of PVC extruders ranges from 0.3 to 0.8 mm).

2. Regularly check the straightness of the screw; if the bending degree exceeds 0.1 mm/m, straightening treatment is required.

3. Starting the screw directly without preheating or with insufficient preheating

• Misoperation Manifestation: Forcing the screw to rotate when the barrel temperature does not reach the set value (e.g., PVC extrusion temperature ranges from 160 to 190℃).

• Hazards: At low temperatures, the material viscosity is high, resulting in a sharp increase in screw rotation resistance, which is prone to motor overload, excessive torque-induced screw fracture, and material caking and barrel blockage.

• Preventive Measures

1. Strictly implement the preheating procedure: Gradually heat up according to the segmented temperature settings of the barrel (feeding section, compression section, homogenization section). After reaching the set temperature, insulate for 20 to 30 minutes to ensure uniform temperature of the barrel and screw.

2. After preheating is completed, manually jog the screw first to check for jamming, and then start it at a low speed.

II. Misoperation Scenarios and Preventive Measures During Operation

1. Sudden increase/decrease of screw speed and frequent emergency stop/start

• Misoperation Manifestation: During production, the screw speed is suddenly adjusted from low to high to pursue output; or the screw is directly stopped in case of slight material blockage.

• Hazards: Sudden speed increase will cause abrupt changes in screw stress and impact loads, which may lead to fatigue fracture of the screw in the long run; emergency stop will cause the materials in the barrel to stop instantly, which are prone to degradation and carbonization at high temperatures, and the screw will be jammed when restarted.

• Preventive Measures

1. When adjusting the screw speed, increase/decrease gradually with an adjustment range of no more than 5r/min each time to avoid sudden speed changes.

2. In case of slight material blockage, first reduce the speed and increase the barrel temperature, then slowly rotate the screw to discharge the blocked material after the material softens; it is strictly prohibited to stop directly. If shutdown is necessary, first reduce the screw speed to 0, then turn off the motor, and manually rotate the screw to discharge residual materials at the same time.

2. Screw idling due to feeding interruption

• Misoperation Manifestation: The hopper is short of materials and not replenished in time, resulting in screw idling and dry friction with the inner wall of the barrel; or foreign objects block the feed inlet during forced feeding, causing screw idling.

• Hazards: Dry friction will quickly wear the wear-resistant layers of the screw and barrel, and the heat generated by idling will cause overheating and degradation of residual materials in the barrel.

• Preventive Measures

1. Install a level sensor to automatically alarm and reduce the screw speed or stop the machine when the hopper is short of materials.

2. Regularly check the feeding device (such as screw feeder) to ensure uniform and stable feeding; it is forbidden to force large pieces of materials into the feed inlet.

3. Overpressure and over-torque operation

• Misoperation Manifestation: Blindly increasing the screw speed or back pressure to improve extrusion output, resulting in the screw torque exceeding the rated value; or forcing the screw to operate without timely handling of mold blockage.

• Hazards: Long-term over-torque operation of the screw will lead to fatigue deformation and fracture, and damage to the motor and reducer at the same time.

• Preventive Measures

1. Install a torque monitoring device on the equipment, set the upper torque limit (usually no more than 80% of the rated torque), and automatically alarm and stop when exceeding the limit.

2. Regularly check the mold runner, clean up accumulated materials and carbonized layers in a timely manner to avoid mold blockage; when adjusting the back pressure, increase it gradually, and fix the parameters after observing the stability of the die head pressure.

4. Forcing continuous production under abnormal conditions

• Misoperation Manifestation: During extrusion, when abnormalities such as poor plasticization of materials (e.g., scorched materials, bubbles), abnormal screw noise and vibration occur, production is continued without shutdown inspection.

• Hazards: Abnormal noise and vibration are usually precursors to screw jamming and bending, and forced production will aggravate equipment damage.

• Preventive Measures

1. Formulate an operation inspection SOP, and check the screw operation status every 30 minutes: listen for abnormal noise, touch to check whether the barrel vibration is normal, and observe whether the appearance of extruded materials is qualified.

2. Stop the machine immediately when abnormalities are detected, troubleshoot the causes (such as material problems, screw wear, mold blockage, etc.), and restart only after troubleshooting.

5. Emergency Response and Misoperation Prevention for Unstable Power Supply and Sudden Power Outages

(1) Core Risks of Sudden Power Outages

(2) Correct Emergency Steps for Sudden Power Outages

(3) Standard Restart Procedures After Power Resumption (to Avoid Misoperations)

1. Inspection and Preparation:

• Clean the residual materials in the hopper and add new materials again (to avoid foreign objects mixed in during power outage);

• Manually rotate the screw (or jog the hand-cranking device) to confirm that there is no jamming of the screw;

• Check whether the electrical system (motor, frequency converter, temperature controller) is normal.

2. Preheating and Temperature Rise:

• Set the temperature of each barrel section according to the PVC/TPU extrusion process requirements, and heat up section by section gradually (feeding section → compression section → homogenization section);

• After reaching the set temperature, insulate for 30 to 40 minutes (10 minutes longer than the normal startup insulation time) to ensure that the residual materials in the barrel are fully softened.

3. Low-speed Startup:

• First jog the screw (start for 1 to 2 seconds each time) to observe whether the screw rotates smoothly and whether there is abnormal noise;

• After confirming no abnormalities, start the screw at the minimum speed (5 to 10r/min). After the materials are stably discharged from the die head, gradually increase the speed to the normal production parameters.

4. Abnormality Troubleshooting:

• Observe the appearance of extruded materials after restarting; if scorched materials and black spots appear, stop the machine immediately and rinse the barrel with transition materials;

• Check the screw torque value; if it exceeds 80% of the rated value, stop the machine to clean the residual solidified materials.

(4) Preventive Measures for Unstable Power Supply

1. Install voltage stabilizers/uninterruptible power supplies (UPS): Provide stable power supply for the extruder control system and heating system to avoid speed out-of-control and temperature control failure caused by voltage fluctuations.

2. Set voltage abnormality protection: Set the upper and lower voltage limit thresholds (such as 380V±10%) in the frequency converter. When the voltage is abnormal, the screw speed will be automatically reduced and an alarm will be issued to avoid screw damage caused by sudden load changes.

3. Formulate a power outage emergency plan: Conduct special training for operators, clarify the operation steps such as hand-cranking the screw and temperature control after power outage, to avoid misoperations due to panic.

   

III. Misoperation Scenarios and Preventive Measures After Shutdown

1. Stopping directly at high temperature without cleaning residual materials in the screw

• Misoperation Manifestation: After production, the machine is stopped directly without discharging the high-temperature materials in the barrel, resulting in cooling and solidification of residual materials, which makes it difficult to start the machine next time, and the materials after high-temperature degradation will corrode the screw.

• Hazards: The solidified residual materials adhere to the screw, which is easy to cause screw jamming when starting the machine next time; the acidic substances in the degraded materials will corrode the screw coating.

• Preventive Measures

1. During normal shutdown, first reduce the screw speed, empty the materials in the barrel, and then stop the machine; for long-term shutdown, rinse with transition materials before stopping.

2. After emergency shutdown, manually rotate the screw to discharge residual materials or disassemble the screw for cleaning after the barrel temperature drops below 100℃.

2. Disassembling the screw without cooling

• Misoperation Manifestation: Disassembling the screw immediately when the temperature of the barrel and screw is still high after shutdown, resulting in screw deformation due to thermal expansion and contraction.

• Hazards: After the high-temperature screw is disassembled, it will shrink rapidly due to the influence of cold air, resulting in bending deformation.

• Preventive Measures

1. After shutdown, wait until the barrel temperature drops below 50℃ before carrying out screw disassembly operations.

2. Place the disassembled screw horizontally on a special bracket, and avoid vertical suspension or stacking to prevent screw bending.

IV. Personnel Operation Specifications and Management Measures

1. Pre-job Training: Formulate the Extruder Screw Operation Manual, add a chapter on emergency operations for sudden power outages, conduct professional training for operators, and only those who pass the assessment can take up their posts. Focus on training startup, shutdown, barrel cleaning procedures and abnormal handling methods.

2. Formulate Standard Operating Procedures (SOPs): Clarify each step of screw operation (such as preheating time, speed adjustment range, inspection frequency, emergency actions for power outages) to avoid arbitrary manual operations.

3. Regular Maintenance: Establish a screw maintenance account, regularly check the screw wear and coating peeling. It is recommended to conduct a comprehensive inspection of PVC/TPU extruders every 3 to 6 months, and replace the screw in a timely manner when wear is severe.

4. Equipment Renovation and Upgrading: Evaluate the feasibility of installing voltage stabilizers and UPS power supplies for the problem of unstable power supply, so as to reduce the damage to equipment caused by sudden power outages.